The present invention relates to an improved method of thermo-compression diffusion bonding together metal surfaces.
Thermo-compression diffusion bonding is a technique for bonding together a pair of opposing metal surfaces under the influence of thermal energy (i.e., heat) and compressional force. A thermo-compression diffusion bond between metal surfaces is characterized as having an interface region where the metal of the metal surfaces diffuses together to form a continuous metal structure. A prior art method for thermo-compression diffusion bonding is disclosed and claimed in U.S. Pat. No. 4,252,263--D. E. Houston, which is assigned to the same assignee as the present application and is incorporated herein by reference.
In the thermo-compression diffusion bonding method of Houston, first and second articles of metal having first and second opposing metal surfaces to be bonded to each other are placed between a pair of parallel metallic plates. The metallic plates are pulled toward each other with bolts whereby the first and second metal surfaces are placed under a compressional force. The entire assembly is then heated to a desired maximum temperature sufficient for thermo-compression diffusion bonding to occur between the first and second metal surfaces. During this heating process, an additional compressional force is exerted between the first and second metal surfaces due to different rates of thermal expansion of the parallel metallic plates and the bolts. Specifically, the metallic plates expand more than the bolts upon heating, thereby imposing an additional compressional force on the first and second metal surfaces. From the foregoing, it can be appreciated that this additional compressional force is dependent upon the heating of the metal surfaces to be bonded. The present inventors have discovered that an improved bond can be obtained by utilizing the present improved method of thermo-compression diffusion bonding. In the improved method, heating of metal surfaces to be bonded is controlled independently of the compressional force pressing these surfaces together.